Understanding HART Dynamic Variables and Their Role in Displaying Measured Variables in DCS
In industrial automation, the Highway Addressable Remote Transducer (HART) protocol is a widely used communication standard that bridges the gap between traditional analog signals and modern digital systems. One of its key features is the Dynamic Variable (DV) Function, which allows multiple process variables to be communicated digitally over a single 4-20 mA signal. This functionality is invaluable for efficiently integrating measurement data into Distributed Control Systems (DCS), enhancing both visibility and control.
This post explains the HART Dynamic Variable function, its benefits in DCS applications, and highlights the major providers of HART-enabled devices.
What Is HART Dynamic Variable Function?
The HART protocol enables a digital overlay on the analog 4-20 mA signal, allowing the transmission of multiple variables and diagnostics. The Dynamic Variable (DV) Function refers to the ability of a HART device to send the following categories of variables:
- Primary Variable (PV):
The main measured parameter, such as flow, pressure, or temperature, sent via the 4-20 mA signal. - Secondary Variable (SV):
An additional process variable, such as temperature or density, communicated digitally. - Tertiary Variable (TV):
A third measured parameter, often related to secondary measurements. - Quaternary Variable (QV):
A fourth measurement or diagnostic value.
These variables can be polled by the DCS or other control systems to provide comprehensive insights into the process.
How HART Dynamic Variables Help in DCS Integration
1. Efficient Use of Resources
- Single Connection for Multiple Data Points:
HART enables the transmission of multiple process variables over a single 4-20 mA connection. This reduces the need for additional wiring and devices, saving cost and simplifying installation.
2. Enhanced Process Visibility
- Real-Time Access to All Variables:
The DCS can poll and display all four dynamic variables (PV, SV, TV, QV), providing operators with a more complete view of the process. - Diagnostics and Alerts:
HART devices can also communicate diagnostic information, such as sensor health or maintenance alerts, improving decision-making.
3. Simplified System Design
- No Need for Additional Instruments:
With multiple variables transmitted from a single device, there’s less need for redundant instruments, reducing complexity. - Standardized Protocol:
HART is supported by nearly all major DCS vendors, ensuring seamless integration and compatibility.
4. Remote Monitoring and Configuration
- Access Through DCS:
Operators can remotely access device settings and diagnostics directly from the DCS, streamlining maintenance and reducing downtime.
Main Applications of HART Dynamic Variables in DCS
- Flow Measurement:
- Devices like Coriolis flow meters can transmit mass flow as the PV and density, temperature, and volume flow as SV, TV, and QV.
- DCS displays all variables for better process control.
- Level Measurement:
- Radar or ultrasonic level transmitters can provide level as the PV and additional variables like distance and signal strength as SV or TV.
- Helps operators monitor tank levels more comprehensively.
- Pressure and Temperature Monitoring:
- Pressure transmitters can communicate absolute pressure (PV), gauge pressure (SV), and temperature (TV).
- Useful in applications like boiler monitoring or compressor systems.
- Environmental Monitoring:
- Gas analyzers using HART can transmit gas concentration (PV) alongside temperature, pressure, and diagnostic information as secondary variables.
Who Provides HART Dynamic Variable Functionality?
Several leading manufacturers offer HART-enabled devices with dynamic variable capabilities. Here are some major players:
1. Emerson
- Key Products:
- Rosemount Transmitters (e.g., 3051 Pressure Transmitter).
- Micro Motion Flow Meters with multivariable outputs.
- Integration Support:
Emerson’s AMS Device Manager and DeltaV DCS seamlessly integrate HART devices, enabling full utilization of dynamic variables.
2. Honeywell
- Key Products:
- SmartLine Transmitters for pressure, temperature, and level measurement.
- HART-compatible analyzers.
- Integration Support:
Honeywell Experion PKS DCS supports advanced HART functionality for real-time diagnostics and multivariable integration.
3. ABB
- Key Products:
- 266 Pressure Transmitters.
- CoriolisMaster Flow Meters with HART capabilities.
- Integration Support:
ABB’s 800xA DCS fully supports HART dynamic variables for enhanced system visibility.
4. Endress+Hauser
- Key Products:
- Proline Promass Flow Meters.
- Cerabar Pressure Transmitters.
- Integration Support:
Endress+Hauser’s FieldCare software and integration with major DCS platforms ensure smooth use of HART dynamic variables.
5. Yokogawa
- Key Products:
- EJX Series Pressure Transmitters.
- Rotamass Coriolis Flow Meters.
- Integration Support:
Yokogawa’s CENTUM VP DCS supports full HART communication, including dynamic variables.
6. Siemens
- Key Products:
- SITRANS Flow Meters and Pressure Transmitters.
- Integration Support:
Siemens SIMATIC PCS 7 system integrates seamlessly with HART devices.
Best Practices for Using HART Dynamic Variables in DCS
- Ensure Compatibility:
Confirm that both the device and the DCS support HART communication and dynamic variables. - Leverage Multivariable Data:
Configure the DCS to poll and display all dynamic variables to maximize process insights. - Utilize Diagnostics:
Take advantage of diagnostic features like sensor health and error alerts to reduce downtime. - Use Smart Software:
Employ software tools (e.g., Emerson AMS or Honeywell Field Device Manager) to configure and monitor HART devices efficiently.
Conclusion
The HART Dynamic Variable Function is a powerful tool for modern industrial automation. By enabling the transmission of multiple variables over a single connection, it simplifies system design, enhances process visibility, and reduces operational costs. Whether you’re monitoring flow, pressure, temperature, or level, HART-enabled devices provide the data and diagnostics needed for optimized performance.
With leading providers like Emerson, Honeywell, ABB, and others offering HART-compatible solutions, integrating these devices into your DCS is easier than ever. By fully utilizing the dynamic variable function, engineers and operators can unlock new levels of efficiency, reliability, and control in their processes. Please refer to the post about how to setup the Hart Dynamic variable Function.